The machine and the therapy concept.

Maintenance haemodialysis became established in mainstream clinical practice in the 1960s. For pragmatic reasons, diffusive dialysis was the technique which underpinned its success. Over the next 15 years it was shown that short- and medium-term survival depended only on a critical level of urea clearance being achieved. Uncomplicated technology with negligible capacity for middle molecule removal could deliver this and the case for developing more sophisticated machines able to broaden the spectrum of solute removal was unconvincing. Dialysis-related amyloidosis which was recognised in the mid-1980s as a devastating complication in long survivors disturbed this complacency. The journey to develop machines which could deliver broad-spectrum solute removal while exposing patients only to ultrapure fluids and biocompatible materials is described elsewhere in this text. The Lister Renal Unit was established in 1988. A fruitful collaboration between the multidisciplinary clinical team and engineering colleagues in the R&D Department of Fresenius contributed to a steady and in-depth understanding of the effect of superimposing convection on diffusive dialysis. From the outset only high-flux dialysis using ultrapure fluids was employed. Haemodiafiltration (HDF) was introduced in 1993. This paper summarises our observations regarding the relative contributions of natural renal function and convective blood purification to long-term outcomes. We have recently reported a 19-year experience which has allowed us to more clearly define the rationale for HDF in modern clinical practice. HDF is an engineering triumph which is likely to universally supersede diffusive dialysis. The challenge for clinicians moving forward is to learn in which treatment schedules this technology can best be deployed to improve the health prospects of patients with kidney failure.